A method and device for improving the discharge regime between two electrodes

Abstract

The invention relates to a method and to a device for improving the dische regime of an electric arc produced between two electrodes. The device is characterized in that it includes means an insulating element (32), preferably spherical in shape, for increasing the resistance to the passage of the electric arc (A) between ends of the electrodes (12, 14). By using the invention it is possible to obtain an arc discharge of the critically damped type. The method and the device are preferably used in shock wave generator apparatus for hydraulic lithotripsy.

We claim: 
     
       1. A method of improving a discharge regime of an electric arc produced in a low electrical resistance fluid medium, said arc being produced in said medium between at least two axially aligned arc-generating electrodes having their free ends disposed in axially spaced apart relation for defining a gap between same, the method comprising increasing the electrical resistance in said gap above the resistance of said fluid medium for modifying the shape of the electrical arc generated therebetween. 
     
     
       2. A method according to claim 1, wherein said step for increasing the electrical resistance in said gap comprises disposing a high resistance insulating element in the gap between the free ends of the electrodes. 
     
     
       3. A method according to claim 2, wherein the resistance of the insulating element is selected in such a manner as to cause said resistance to give rise to an arc discharge of a critically damped type. 
     
     
       4. A method according to claim 2, wherein the step of disposing a high resistance insulating element in said gap further comprises selecting the shape of the insulating element in such a manner as to ensure that the arc is substantially spherical in shape. 
     
     
       5. The method of claim 1, wherein the medium is a liquid. 
     
     
       6. A device for improving a discharge regime of an electric arc produced in a low electrical resistance medium between at least two axially aligned arc-generating electrodes having their free ends disposed in axially spaced apart relation for defining a gap therebetween, the device comprising means for increasing the electrical resistance in said gap above the electrical resistance of said medium, thereby modifying the shape of the electrical arc generated between the free ends of the electrodes. 
     
     
       7. A device according to claim 6, wherein the means for increasing the electrical resistance in said gap comprises a high resistance insulating element interposed in the gap. 
     
     
       8. A device according to claim 7, wherein the resistance of the insulating element is selected to induce an arc discharge of an essentially critically damped type. 
     
     
       9. The device of claim 6, wherein the medium is a liquid. 
     
     
       10. A device for improving a discharge regime of an electric arc produced in a low electrical resistance medium, said electric arc being produced between at least two axially aligned, arc-generating electrodes having their free ends disposed in axially spaced apart relation for defining a gap therebetween, said device comprising a high resistance insulating element interposed in said gap between the free ends of the electrodes, the insulating element being substantially spherical in shape. 
     
     
       11. A device according to claim 10, wherein the insulating element includes two electrode-positioning cavities defined by bottom walls, such that when the free ends of the electrodes are in abutment against the bottom walls of the cavities, the free ends of the electrodes converge symmetrically about a focus point on which the electric arc is to be centered. 
     
     
       12. A shock wave generator apparatus comprising a truncated ellipsoidal reflector having a first focus internal to said reflector and a second focus lying outside said reflector, said reflector being filled with a low electrical resistance liquid; at least two axially aligned, arc-generating electrodes having their free ends disposed in axially spaced apart relation for defining a gap therebetween, said free ends of said electrodes being immersed in said liquid; a high electrical resistance insulating element interposed in the gap between the free ends of the electrodes; and a support means mounted inside said truncated ellipsoidal reflector for supporting said insulating element. 
     
     
       13. The shock wave generator of claim 12, wherein the insulating element has a geometric center located in coincidence with the internal focus of the ellipsoidal reflector. 
     
     
       14. The shock wave generator apparatus of claim 12, wherein the insulating element is substantially spherical in shape. 
     
     
       15. The shock wave generator of claim 12, wherein the liquid is water. 
     
     
       16. A shock wave generator apparatus for generating a shock wave by generating an electric arc between arc-generating electrodes, said apparatus comprising a chamber filled with a low electrical resistance liquid, two arc-generating electrodes axially aligned and having their free ends disposed in axially spaced apart relation for defining a gap therebetween, at least said free ends of the electrodes being disposed in said liquid in said chamber, said apparatus further comprising means for increasing the electrical resistance in said gap between the free ends of the electrodes for modifying the shape of the electrical arc generated therebetween. 
     
     
       17. A shock wave generator apparatus for generating a shock wave by generating an electric arc between two arc-generating electrodes, said apparatus comprising a chamber filled with a low electrical resistance liquid two arc-generating electrodes axially aligned and having their free ends disposed in axially spaced apart relation for defining a gap therebetween, said free ends of the electrodes being disposed in said liquid in said chamber, said apparatus further comprising a high resistance insulating element interposed in said gap between the free ends of the electrodes, said insulating element constituting an obstacle to the direct passage of the electric arc between the free ends of the electrodes. 
     
     
       18. A shock wave generator apparatus according to claim 17, wherein said chamber includes a truncated ellipsoidal reflector, a support means comprising a rod mounted inside said truncated ellipsoidal reflector for supporting said insulating element, and said high resistance insulating element having a center with the center of the insulating element coinciding with the internal focus of the ellipsoidal reflector. 
     
     
       19. In a process for generating a shock wave in a shock wave generator by generating an electric arc between two electrodes, said electrodes being axially aligned and having their free ends disposed in axially spaced apart relation for defining a gap therebetween, the free ends of the electrodes being immersed in a low electrical resistance liquid medium, wherein the improvement comprises a step of increasing the electrical resistance in said gap between the free ends of the electrodes thereby modifying the shape of the electrical arc generated therebetween.